It is a common practice to reinforce such rigid plastics as polyvinyl chloride, polymethyl methacrylate, polystyrene, styrene-acrylonitrile copolymers and the like with particles of rubber polymers such as polybutadiene and the polyacrylates. The addition of rubber to these common plastics improves their impact strength, that is their ability to withstand a rapidly applied shock. While the addition of rubber improves the impact strength of these particles, their other physical properties such as tensile strength, clarity, heat distortion temperature, hardness and aging stability are, however, adversely affected by the rubber.
A procedure which is often used to reinforce such hard, brittle polymers involves their preparation in the presence of rubbers. The products resulting from such polymerization procedures which are referred to as interpolymers or graft copolymers, normally have rubber contents of about 20-60%. These high rubber content materials are employed as so-called "impact modifiers" by being blended with brittle plastics in order to enhance their impact strength. The rubber content of these blends is generally about 5-25%. For example, styrene-acrylonitrile, i.e., "SAN," monomers are commonly polymerized in the presence of polybutadiene rubbers at about a 50/50 SAN to rubber ratio. The resulting graft copolymer is then blended with a conventional styrene-acrylonitrile copolymer to a rubber content of about 10-20% so as to produce ABS type plastics.